Bridge measuring apparatus of the above kind have been known for some time. These apparatus usually have lateral parts which are elevated relative to the measuring pad. A bridge is movably guided in the horizontal direction on the lateral parts and spans the measuring pad. A so-called transverse carriage is movably guided in a second horizontal coordinate direction along the bridge. The transverse carriage, in turn, movably guides a spindle vertically in the third coordinate direction. A probe is disposed at the lower end of the spindle and measurements of a workpiece clamped to the measuring pad can be made therewith.
Bridge measuring apparatus of this kind afford the special advantage relative to other coordinate measuring apparatus such as the portal measuring apparatus or the stand measuring apparatus in that the guides are clearly above the measuring pad so that they are relatively well protected against contamination. Coordinate measuring apparatus in bridge configuration are designed for use under rough ambient conditions such as in manufacturing because of this feature.
Nonetheless, coordinate measuring apparatus having a bridge configuration are relatively seldom utilized notwithstanding their special advantages because experience has shown that the lateral parts, on which the bridge is movably supported, expand differently with large temperature gradients so that the guides are no longer precisely horizontally aligned. This can lead to significant measurement errors.